Interworking between mobile railway networks and gsm networks

ABSTRACT

A server receives a call request for a mission critical, push to talk (MCPTT) call. In response to receiving the call request, the server accesses a mapping of an MCPTT identifier of a user equipment with an interworking identifier that is formed according to an address format implemented in Global System for Mobile communications (GSM) for Railways (GSM-R). The server then forwards the call request from the server based on the mapping. In some cases, the MCPTT identifier is a uniform resource identifier (URI) and the interworking identifier is represented in an e164 format.

BACKGROUND

Mission critical, push to talk (MCPTT) refers to a PTT productfunctionality that meets the requirements of Public Safetymission-critical voice communication, which include highavailability/reliability, low latency, support for group calls and 1:1calls, talker identification, device-to device (D2D) directcommunication, emergency calling, clear audio quality, and the like. Inconjunction with other organizations, the Third Generation PartnershipProject (3GPP) is developing standards for implementing MCPTT overnetworks that operate according to the Long Term Evolution (LTE)standards and Fifth Generation (5G) defined by the 3GPP. The MCPTTstandards for LTE/5G operation address call types, floor control,priority, preemption, performance, group management, off-network use,security, interworking with non-LTE PTT systems, and the like.Communication within railway systems is an important application and3GPP is currently developing a mobile communication system for railwaysthat is based on MCPTT. A user equipment in a railway mobilecommunication system establishes a session using an applicationimplemented on the user equipment, which communicates with an MCPTTserver that connects to an LTE core network. The MCPTT system isrequired to interconnect and interoperate with other networks, e.g., tosupport communication in numerous regions traversed by a railway system.Implementing MCPTT without interoperability would severely impact voicecommunications where coverage is poor or in regions that choose othervendors that implement different networks. Thus, limitedinteroperability would reduce the value of the MCPTT system to railwayorganizations.

SUMMARY

The following presents a simplified summary of the disclosed subjectmatter in order to provide a basic understanding of some aspects of thedisclosed subject matter. This summary is not an exhaustive overview ofthe disclosed subject matter. It is not intended to identify key orcritical elements of the disclosed subject matter or to delineate thescope of the disclosed subject matter. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

In some embodiments, an apparatus is provided that includes atransceiver configured to receive a call request for a mission critical,push to talk (MCPTT) call and a processor configured to access, inresponse to receiving the call request, a mapping of an MCPTT identifierof a user equipment with an interworking identifier that is formedaccording to an address format implemented in Global System for Mobilecommunications (GSM) for Railways (GSM-R). The transceiver forwards thecall request based on the mapping.

In some embodiments, the MCPTT identifier is a uniform resourceidentifier (URI) and the interworking identifier is represented in ane164 format.

In some embodiments, the mapping is stored in a user profile thatincludes a binding between the MCPTT identifier, the interworkingidentifier, and an identifier of the apparatus.

Some embodiments of the apparatus include a memory configured to storethe user profile in a routing table, wherein the processor is configuredto access the mapping from the memory.

Some embodiments of the processor are configured to access the mappingfrom a database that is implemented external to the apparatus.

Some embodiments of the transceiver are configured to receive the callrequest including the MCPTT identifier in response to the user equipmentinitiating the MCPTT call. Some embodiments of the processor areconfigured to add the interworking identifier to the call request priorto forwarding the call request to an interworking function associatedwith a GSM-R system.

In some embodiments, the interworking identifier is displayed to a GSM-Rclient or used to initiate another call to the user equipment by theGSM-R client.

Some embodiments of the transceiver are configured to receive the callrequest including an identifier in the address format implemented inGSM-R in response to a GSM-R client initiating a call.

Some embodiments of the processor are configured to resolve theidentifier into the MCPTT identifier of the user equipment, and whereinthe transceiver is configured to forward the call request to the userequipment based on the MCPTT identifier.

In some embodiments, a method is provided that includes receiving, at aserver, a call request for a mission critical, push to talk (MCPT) calland accessing, from the server and in response to receiving the callrequest, a mapping of an MCPTT identifier of a user equipment with aninterworking identifier that is formed according to an address formatimplemented in Global System for Mobile communications (GSM) forRailways (GSM-R). The method also includes forwarding the call requestfrom the server based on the mapping.

In some embodiments of the method, the MCPTT identifier is a uniformresource identifier (URI) and the interworking identifier is representedin an e164 format.

Some embodiments of the method include storing the mapping in a userprofile that includes a binding between the MCPTT identifier, theinterworking identifier, and an identifier of the server.

In some embodiments of the method, storing the mapping in the userprofile includes storing the user profile in a routing table implementedin the server and accessing the mapping includes accessing the mappingfrom the user profile.

In some embodiments of the method, accessing the mapping includesaccessing the mapping from a database that is implemented external tothe server.

Some embodiments of the method include receiving, at the server, thecall request including the MCPTT identifier in response to the userequipment initiating the MCPTT call, adding, at the server, theinterworking identifier to the call request, and forwarding, from theserver, the call request to an interworking function associated with aGSM-R system.

Some embodiments of the method include displaying the interworkingidentifier to a GSM-R client.

Some embodiments of the method include receiving, at the server, another call request from a GSM-R client to initiate another call to theuser equipment, wherein the other call request includes the interworkingidentifier.

Some embodiments of the method include receiving, at the server, thecall request including an identifier in the address format implementedin GSM-R in response to a GSM-R client initiating a call.

Some embodiments of the method include resolving, at the server, theidentifier into the MCPTT identifier of the user equipment andforwarding, from the server, the call request to the user equipmentbased on the MCPTT identifier.

In some embodiments, an apparatus is provided that includes means forreceiving, at a server, a call request for a mission critical, push totalk (MCPTT) call and means for accessing, from the server and inresponse to receiving the call request, a mapping of an MCPTT identifierof a user equipment with an interworking identifier that is formedaccording to an address format implemented in Global System for Mobilecommunications (GSM) for Railways (GSM-R). The apparatus also includesmeans for forwarding the call request from the server based on themapping.

In some embodiments of the apparatus, the MCPTT identifier is a uniformresource identifier (URI) and the interworking identifier is representedin an e164 format.

Some embodiments of the apparatus include means for storing the mappingin a user profile that includes a binding between the MCPTT identifier,the interworking identifier, and an identifier of the server.

Some embodiments of the apparatus include means for storing the userprofile in a routing table implemented in the server and accessing themapping includes accessing the mapping from the user profile.

Some embodiments of the apparatus include means for accessing themapping from a database that is implemented external to the server.

Some embodiments of the apparatus include means for receiving the callrequest including the MCPTT identifier in response to the user equipmentinitiating the MCPTT call, means for adding the interworking identifierto the call request, and means for forwarding the call request to aninterworking function associated with a GSM-R system.

Some embodiments of the apparatus include means for displaying theinterworking identifier to a GSM-R client.

Some embodiments of the apparatus include means for receiving, at theserver, an other call request from a GSM-R client to initiate anothercall to the user equipment. The other call request includes theinterworking identifier.

Some embodiments of the apparatus include means for receiving, at theserver, the call request including an identifier in the address formatimplemented in GSM-R in response to a GSM-R client initiating a call.

Some embodiments of the apparatus include means for resolving, at theserver, the identifier into the MCPTT identifier of the user equipmentand forwarding, from the server, the call request to the user equipmentbased on the MCPTT identifier.

In some embodiments, an apparatus is provided that includes at least oneprocessor and at least one memory including computer program code. Theat least one memory and the computer program code are configured to,with the at least one processor, cause the apparatus at least to performreceiving a call request for a mission critical, push to talk (MCPTT)call. The at least one memory and the computer program code are alsoconfigured to, with the at least one processor, cause the apparatus atleast to perform accessing, in response to receiving the call request, amapping of an MCPTT identifier of a user equipment with an interworkingidentifier that is formed according to an address format implemented inGlobal System for Mobile communications (GSM) for Railways (GSM-R) andforwarding the call request based on the mapping.

In some embodiments of the apparatus, the MCPTT identifier is a uniformresource identifier (URI) and the interworking identifier is representedin an e164 format.

Some embodiments of the apparatus include means for storing the mappingin a user profile that includes a binding between the MCPTT identifier,the interworking identifier, and an identifier of the server.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform storing the user profile in a routingtable implemented in the server and accessing the mapping includesaccessing the mapping from the user profile.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform accessing the mapping from a database thatis implemented external to the server.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform receiving the call request including theMCPTT identifier in response to the user equipment initiating the MCPTTcall, adding the interworking identifier to the call request, andforwarding the call request to an interworking function associated witha GSM-R system.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform displaying the interworking identifier toa GSM-R client.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform receiving, at the server, an other callrequest from a GSM-R client to initiate another call to the userequipment. The other call request includes the interworking identifier.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform receiving, at the server, the call requestincluding an identifier in the address format implemented in GSM-R inresponse to a GSM-R client initiating a call.

In some embodiments, the at least one memory and the computer programcode are configured to, with the at least one processor, cause theapparatus at least to perform resolving, at the server, the identifierinto the MCPTT identifier of the user equipment and forwarding, from theserver, the call request to the user equipment based on the MCPTTidentifier.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings. The use of the same referencesymbols in different drawings indicates similar or identical items.

FIG. 1 is a block diagram of a communication system according to someembodiments.

FIG. 2 is a block diagram of a communication system that supportsinterworking between an MCPTT system and a GSM-R system according tosome embodiments.

FIG. 3 is a block diagram of a database that maps identifiers of anMCPTT server and MCPTT user equipment to an interworking identifieraccording to some embodiments.

FIG. 4 is a message flow used to convey call requests over an uplinkfrom an MCPTT system to a GSM-R system according to some embodiments.

FIG. 5 is a message flow used to convey call requests over a downlinkfrom a GSM-R system to an MCPTT system according to some embodiments.

FIG. 6 is a block diagram of a communication system that includes aMCPTT server in communication with an MCPTT client and a GSM-R serveraccording to some embodiments.

DETAILED DESCRIPTION

An important example of an outside network for a railway mobilecommunication system is a Global System for Mobile communications (GSM)network that provides services to railways (GSM-R). The GSM-R standardsdefine a secure platform for voice and data communication betweenrailway operational staff including drivers, dispatchers, shunting teammembers, train engineers, station controllers, and the like. GSM-Rimplements features including group calls, voice broadcast,location-based connections, and call preemption in case of an emergency.However, interoperability between GSM-R and MCPTT systems is limited orprevented because GSM-R and MCPTT systems use different addressingschemes to identify user equipment in the corresponding systems. TheGSM-R system identifies user equipment and users with numbers that aredefined according to the e164 format, e.g., a maximum of fifteen digitsincluding up to three digits for a country code and twelve digits for asubscriber number. The MCPTT system implements a scheme based on uniformresource identifiers (URI) that identify user equipment and users usinga set of letters or numbers to identify a scheme (e.g., sip, http,https, ldap, mailto, and the like), a path, a query, or a fragment of apage. For example, a user “John Doe” can be identified by the URI:john.doe@example.com.

FIGS. 1-6 disclose techniques to support interoperability between anMCPTT based railway mobile communication system and a GSM-R system bystoring information associating an MCPTT identifier of a user equipmentor a user with an interworking identifier that is formed according tothe address format implemented in GSM-R. The MCPTT identifier is auniform resource identifier (URI) and the interworking identifier isrepresented in the e164 format. A user profile for the user equipmentincludes a binding between the MCPTT identifier, the interworkingidentifier, and an MCPTT server. In some embodiments, the user profileis configured as part of a registration procedure performed by the userequipment and the MCPTT server. The user profile is stored in a routingtable in the MCPTT server or an external database that is queried basedon an identifier of the MCPTT server.

In response to the user equipment initiating a call, the call request isforwarded to the MCPTT server, which adds the interworking identifier tothe call request. For example, the interworking identifier can beencoded into the body of the request. The call request including theinterworking identifier is then forwarded to an interworking function,which forwards the call request to a GSM-R client. Some embodiments ofthe GSM-R client display the interworking identifier to the user toallow the user to identify the calling party. In some cases, the GSM-Rclient initiates a return call to the user equipment in the MCPTT basedrailway mobile communication system using the interworking identifier.In response to the GSM-R client initiating a call, a call requestincluding an identifier of the user equipment in the e164 format isforwarded to an interworking function that identifies a correspondingMCPTT server. The call request is then forwarded from the interworkingfunction to the MCPTT server. The identifier in the call requestcorresponds to an interworking identifier of the user equipment. TheMCPTT server resolves the e164 address into the MCPTT identifier of theuser equipment. The call request is then forwarded to the user equipmentbased on the MCPTT identifier.

FIG. 1 is a block diagram of a communication system 100 according tosome embodiments. The communication system 100 includes a server 105that supports mission critical, push to talk (MCPTT) applications. Asused herein, the term MCPTT refers to a PTT product functionality thatmeets the requirements of Public Safety mission-critical voicecommunication, which include high availability/reliability, low latency,support for group calls and 1:1 calls, talker identification, device-todevice (D2D) direct communication, emergency calling, clear audioquality, and the like. Some embodiments of the MCPTT server 105implement MCPTT according to the Long Term Evolution (LTE) standards andFifth Generation (5G) defined by the Third Generation PartnershipProject (3GPP) in conjunction with other organizations. The MCPTTstandards for LTE/5G operation address call types, floor control,priority, preemption, performance, group management, off-network use,security, interworking with non-LTE PIT systems, and the like.

The MCPTT server 105 provides the MCPTT service via one or more basestations 110 that establish wireless connections with one or more userequipment 115 over an air interface 120. The user equipment 115 (orcorresponding users) are identified by an MCPTT identifier. In someembodiments, the MCPTT identifier is a URI that identifies the userequipment 115 (or the corresponding user) using a set of letters ornumbers to identify a scheme, a path, a query, or a fragment of a page.For example, the user equipment 115 can be identified by the URI:johnsUE@example.com. For another example, a user “John Doe” can beidentified by the URI: john.doe@example.com. Call requests transmittedby the user equipment 115 to the MCPTT server 105 include the MCPTTidentifier and the MCPTT server 105 uses the MCPTT identifier to routecall requests to the user equipment 115.

The communication system 100 also includes a server 125 that isimplemented as a part of a railway mobile communication system thatprovides communication to users or user equipment in a railway system,e.g., users or user equipment on one or more trains 130. Someembodiments of the GSM-R server 125 operate according to the GSM-Rstandards. The GSM-R server 125 establishes wireless connections withusers or user equipment on the train 130 via a base station 135 over anair interface 140. In some embodiments, the wireless connection betweenthe users or user equipment on the train 130 and the base station 135 isestablished in a predetermined standard GSM-R band in the range 876-880MHz for uplink data transmission and 921-925 MHz for downlink datatransmission, although other frequency bands are used for GSM-R in otherregions. The user equipment (or users) on the train 130 identified by aGSM identifier or MSISDN that is defined according to the e164 format,e.g., a maximum of fifteen digits including up to three digits for acountry code and twelve digits for a subscriber number. For example,user equipment (or corresponding user) on the train 130 can beidentified by a phone number such as +49 (089) 1234-5678.

The MCPTT server 105 and the GSM-R server 125 communicate over aninterface 145. Some embodiments of the interface 145 are implementedusing an interworking function, as discussed below. However, callrequests for MCPTT services cannot be directly exchanged between theuser equipment 115 and user equipment (or users) on the train 130because the user equipment 115 in the MCPTT system and the userequipment (or users) in the GSM-R system do not use the same format fortheir identifiers. An interworking identifier having the same format asthe GSM identifiers used in the GSM-R system (e.g., the e164 format) istherefore assigned to the user equipment 115 to facilitate communicationwith other user equipment (or users) in the GSM-R system. The MCPTTserver 105 receives call requests for MCPTT calls from either the userequipment 115 or the user equipment (or users) in the GSM-R system. Inresponse to receiving the call request, the MCPTT server 105 accesses amapping that associates the MCPTT identifier within interworkingidentifier. The call request is then forwarded based on the interworkingidentifier. Some embodiments of the MCPTT server 105 incorporate theinterworking identifier into call requests received from the userequipment 115 on the uplink. Some embodiments of the MCPTT server 105use the interworking identifier to route call requests to the userequipment 115 on the downlink.

FIG. 2 is a block diagram of a communication system 200 that supportsinterworking between an MCPTT system 205 and a GSM-R system 210according to some embodiments. The MCPTT system 205 includes someembodiments of the MCPTT server 105 shown in FIG. 1. The GSM-R system210 includes some embodiments of the GSM-R server 125 shown in FIG. 1.Interworking between the MCPTT system 205 and the GSM-R system 210 isperformed, at least in part, according to the 3GPP Technical Report23.796. In the illustrated embodiment, the communication system 200includes an interworking function 215 to support interworking betweenthe MCPTT system 205 and the GSM-our system 210.

The MCPTT system 205 and the GSM-R system 210 use different addressingschemes. The MCPTT system 205 provides wireless connectivity to an MCPTTuser equipment 220 that is identified by an MCPTT identifier in the URIformat. The GSM-R system 210 provides wireless connectivity to a GSM-Ruser equipment 225 that is identified by a GSM identifier or MSISDN inthe e164 format. An interworking identifier is therefore assigned to theMCPTT user equipment 220 to make the MCPTT user equipment 220 reachablefrom within the GSM-R system 210. The interworking identifier complieswith the requirements for numbering and routing in the GSM-R system 210and is therefore based on MSISDN, i.e., the interworking identifier isdefined in the e164 format. The interworking identifier allows the MCPTTuser equipment 220 to be reached within the MCPTT system 205. Theinterworking identifier is also used by the GSM-R system 210 to set upcommunication towards the MCPTT system 205.

The interworking identifier for the MCPTT user equipment 220 isadministered as a part of configuration of a user profile for a userassociated with the MCPTT user equipment 220. In some embodiments, userprofile configuration is performed according to mechanisms defined inthe 3GPP Technical Specification 24.484. Proprietary configurationtechniques can also be used to configure the user profile. Configurationof the MCPTT user equipment 220 includes generating a binding betweenthe interworking identifier, the MCPTT identifier of the user equipment220, and an address of the MCPTT server 205. Some embodiments of theMCPTT server 205 store the binding in an internal database. The bindingcan also be stored in an external database 230 that is accessible by theMCPTT server 205.

Once configured, the MCPTT user equipment 220 includes the interworkingidentifier in call control signaling towards the GSM-R user equipment225. The included interworking identifier is used to identify the MCPTTuser equipment 220. The GSM-R user equipment 225 uses the interworkingidentifier to identify its communication partner. The identity of thecommunication partner can then be displayed to a user of the GSM-R userequipment 225, e.g., using a caller identification application. Someembodiments of the GSM-R user equipment 225 generate responses such ascallback requests to the MCPTT user equipment 220 based on theinterworking identifier received from the MCPTT user equipment 220. Theinterworking identifier is also used in call control signaling toaddress information for communication from the GSM-R system 210 towardsthe MCPTT system 205.

The interworking identifier therefore supports reachability of the MCPTTuser equipment 220 from the GSM-R system 210. The interworkingidentifier is also available for display on the GSM-R user equipment 225to identify the calling party. The MCPTT server 205 manages theinterworking identifier, which reduces the possibility of fraud and doesnot require that the MCPTT user equipment 220 become responsible forincluding or managing the interworking identifier.

FIG. 3 is a block diagram of a database 300 that maps identifiers of anMCPTT server and MCPTT user equipment to an interworking identifieraccording to some embodiments. The database 300 is stored in someembodiments of the MCPTT server 105 shown in FIG. 1, the MCPTT system205 shown in FIG. 2, and the external database 230 shown in FIG. 2. Therows in the database 300 represent the entries in the database 300 andthe columns indicate the different identifiers. The MCPTT serveridentifier for each entry is stored in the column 305, the MCPTT userequipment identifier is stored in the column 310, and the interworkingidentifier that is assigned to the MCPTT user equipment is stored in thecolumn 315. The entries represent a mapping or a binding between theidentifiers associated with different user equipment. For example, theentry for a first user equipment indicates that it is served by theMCPTT server 00001 and the entry identifies the first user equipmentusing the MCPTT identifier john.doe@example.com. The MCPTT serveridentifier and the MCPTT identifier are mapped to an interworkingidentifier in the e164 format: +49 (089) 1234-5678. For another example,the entry for a second user equipment indicates that it is served by theMCPTT server 00001 and the entry identifies the second user equipmentusing the MCPTT identifier jane.doe@example.com. The MCPTT serveridentifier and the MCPTT identifier for the second user equipment aremapped to an interworking identifier in the e164 format: +49 (089)5678-1234.

FIG. 4 is a message flow 400 used to convey call requests over an uplinkfrom an MCPTT system 405 to a GSM-R system 410 according to someembodiments. The MCPTT system 405 represents some embodiments of theMCPTT system 205 shown in FIG. 2. The MCPTT system 405 includes a clientand a server such as the user equipment 115 and the server 105,respectively, shown in FIG. 1. The GSM-R system 210 includes a serverand a user such as the GSM-R system 210 and the GSM-R user equipment225, respectively, shown in FIG. 2.

At block 415, the MCPTT client registers with the MCPTT server. Duringthe registration process, the MCPTT server attempts to locate a userprofile for the MCPTT client. If the MCPTT server is unable to locate apreviously created user profile, the MCPTT server creates a new userprofile and associates the user profile with the MCPTT client. Aninterworking identifier is assigned to the MCPTT client (eitherpreviously or during the registration process at block 415). Theinterworking identifier is an MSISDN in e164 format. The MCPTT servercreates a binding between an MCPTT identifier of the MCPTT client, theinterworking identifier, and the identifier of the MCPTT server. Thebinding, which represents a mapping between the MCPTT identifier, theinterworking identifier, and the identifier of the MCPTT server, isstored internally by the MCPTT server or an external database.

The MCPTT client initiates a call at block 420. The call is towards theGSM-R client in the GSM-R system 410. The MCPTT client thereforetransmits a call request 425 that includes the MCPTT identifier of theMCPTT client and an identifier of the GSM-R client, such as an MSISDN ine164 format. The message 425 is received at the MCPTT server.

At block 430, the MCPTT server accesses a user profile for the MCPTTclient based on the MCPTT identifier included in the call request 425.The user profile includes (at block 430) the interworking identifierthat is assigned to the MCPTT client. The MCPTT server adds theinterworking identifier into an outgoing call request 435. In someembodiments, the MCPTT server incorporates the interworking identifierinto the body of the call request 435, e.g., as part of anapplication/vnd3gpp.mcptt-info+xml MIME body or any other suitableinformation element. The MCPTT server transmits the call request 435including the interworking identifier to an interworking function (IWF),which forwards the call request 440 to the server in the GSM-R system410. The server then forwards the call request 445 including theinterworking identifier to the user in the GSM-R system 410.

The user in the GSM-R system 410 uses the interworking identifier as anindicator of the identity of the calling party, which in this case isthe client in the MCPTT system 405. Some embodiments of the user displaythe interworking identifier at block 450, although this step is notnecessarily performed as indicated by the dashed outline. Someembodiments of the user initiate a call back (at block 455) based on theinterworking identifier. For example, the user can initiate a privatecall to the client in the MCPTT system 405 using the interworkingidentifier associated with the client and received in the call request445.

FIG. 5 is a message flow 500 used to convey call requests over adownlink from a GSM-R system 505 to an MCPTT system 510 according tosome embodiments. The MCPTT system 510 represents some embodiments ofthe MCPTT system 205 shown in FIG. 2. The MCPTT system 510 includes aclient and a server such as the user equipment 115 and the server 105,respectively, shown in FIG. 1. The GSM-R system 505 includes a serverand a user such as the GSM-R system 210 and the GSM-R user equipment225, respectively, shown in FIG. 2.

At block 515, the MCPTT client registers with the MCPTT server. Asdiscussed above, during the registration process, the MCPTT serveraccesses or creates a user profile that includes an interworkingidentifier that is assigned to the MCPTT client. The interworkingidentifier is an MSISDN in e164 format. The MCPTT server creates abinding between an MCPTT identifier of the MCPTT client, theinterworking identifier, and the identifier of the MCPTT server, whichis stored internally by the MCPTT server or in an external database.

The GSM-R client transmits a call request 520 that is addressed to theMCPTT client using the interworking identifier. For example, the GSM-Rclient can use an MSISDN in e164 format (e.g., the interworkingidentifier) as a destination address for the MCPTT client during thecall set up procedure. The call request 520 is transmitted to the GSM-Rserver, which forwards the call request 525 to an interworking function(IWF).

The interworking function analyzes (at block 530) addressing informationin the call request 525 received from the GSM-R server to identify theMCPTT server that serves the called party. Some embodiments of theinterworking function identify the MCPTT server using an entry in arouting table that maps the called party information included in thecall request 525 to the MCPTT server. Some embodiments of theinterworking function identify the serving MCPTT server using anexternal database. In that case, the interworking function queries theexternal database to determine the address of the MCPTT server thatserves the MCPTT user equipment. Entries in the external databaseinclude a binding MCPTT identifier, the interworking identifier, and theidentifier of the MCPTT server. The interworking function then forwardsthe call request 535 to the MCPTT server based on the identifier.

In response to receiving the call request 535, the MCPTT server resolvesthe interworking identifier included in the call request 535 into theMCPTT identifier of the MCPTT user. As discussed herein, the MCPTTserver resolves the interworking identifier using a mapping stored in aninternal database or an external database. The MCPTT server thenforwards a call request 540 to the MCPTT client using the MCPTTidentifier. The MCPTT client provides an indication of the incoming call(at block 545) in response to receiving the call request 540.

FIG. 6 is a block diagram of a communication system 600 that includes aMCPTT server 605 in communication with an MCPTT client 610 and a GSM-Rserver 615 according to some embodiments. The MCPTT server 605 is usedto implement some embodiments of the MCPTT server 105 shown in FIG. 1and the MCPTT system 205 shown in FIG. 2. In some embodiments, the MCPTTserver 605 accesses an external database 620. The MCPTT server 605includes a transceiver 625 that transmits or receives messages such ascall requests exchanged with the GSM-R server 615 or queries andresponses exchanged with the database 620. Some embodiments of thetransceiver 625 are implemented using a transmitter and a receiver. TheMCPTT server 605 includes memory 630 for storing information such asprocessor instructions, data, and the like. A processor 635 is used toprocess information for transmission, process received information, orperform other operations as discussed herein, e.g., by executinginstructions stored in the memory 630. The MCPTT server 605 is thereforeable to implement some embodiments of the message flows 400 and 500shown in FIGS. 4 and 5, respectively.

The GSM-R server 615 is used to implement some embodiments of the GSM-Rserver 125 shown in FIG. 1 and the GSM-R system 210 shown in FIG. 2. TheGSM-R server 615 includes a transceiver 640 that transmits or receivesmessages such as call requests exchanged with the MCPTT server 605 or aGSM-R client 645. Some embodiments of the transceiver 640 areimplemented using a transmitter and a receiver. The GSM-R server 615includes memory 650 for storing information such as processorinstructions, data, and the like. A processor 655 is used to processinformation for transmission, process received information, or performother operations as discussed herein, e.g., by executing instructionsstored in the memory 650. The GSM-R server 615 is therefore able toimplement some embodiments of the message flows 400 and 500 shown inFIGS. 4 and 5, respectively.

In some embodiments, certain aspects of the techniques described abovemay implemented by one or more processors of a processing systemexecuting software. The software comprises one or more sets ofexecutable instructions stored or otherwise tangibly embodied on anon-transitory computer readable storage medium. The software caninclude the instructions and certain data that, when executed by the oneor more processors, manipulate the one or more processors to perform oneor more aspects of the techniques described above. The non-transitorycomputer readable storage medium can include, for example, a magnetic oroptical disk storage device, solid state storage devices such as Flashmemory, a cache, random access memory (RAM) or other non-volatile memorydevice or devices, and the like. The executable instructions stored onthe non-transitory computer readable storage medium may be in sourcecode, assembly language code, object code, or other instruction formatthat is interpreted or otherwise executable by one or more processors.

A computer readable storage medium may include any storage medium, orcombination of storage media, accessible by a computer system during useto provide instructions and/or data to the computer system. Such storagemedia can include, but is not limited to, optical media (e.g., compactdisc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media(e.g., floppy disc, magnetic tape, or magnetic hard drive), volatilememory (e.g., random access memory (RAM) or cache), non-volatile memory(e.g., read-only memory (ROM) or Flash memory), ormicroelectromechanical systems (MEMS)-based storage media. The computerreadable storage medium may be embedded in the computing system (e.g.,system RAM or ROM), fixedly attached to the computing system (e.g., amagnetic hard drive), removably attached to the computing system (e.g.,an optical disc or Universal Serial Bus (USB)-based Flash memory), orcoupled to the computer system via a wired or wireless network (e.g.,network accessible storage (NAS)).

As used herein, the term “circuitry” may refer to one or more or all ofthe following:

-   -   (a) hardware-only circuit implementations (such as        implementations and only analog and/or digital circuitry) and    -   (b) combinations of hardware circuits and software, such as (as        applicable):        -   (i) a combination of analog and/or digital hardware            circuit(s) with software/firmware and        -   (ii) any portions of a hardware processor(s) with software            (including digital signal processor(s), software, and            memory(ies) that work together to cause an apparatus, such            as a mobile phone or server, to perform various functions)            and    -   (c) hardware circuit(s) and/or processor(s), such as a        microprocessor(s) or a portion of a microprocessor(s), that        requires software (e.g., firmware) for operation, but the        software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in thisapplication, including in any claims. As a further example, as used inthis application, the term circuitry also covers an implementation ofmerely a hardware circuit or processor (or multiple processors) orportion of a hardware circuit or processor and its (or their)accompanying software and/or firmware. The term circuitry also covers,for example and if applicable to the particular claim element, abaseband integrated circuit or processor integrated circuit for a mobiledevice or a similar integrated circuit in a server, a cellular networkdevice, or other computing or network device.

Note that not all of the activities or elements described above in thegeneral description are required, that a portion of a specific activityor device may not be required, and that one or more further activitiesmay be performed, or elements included, in addition to those described.Still further, the order in which activities are listed are notnecessarily the order in which they are performed. Also, the conceptshave been described with reference to specific embodiments. However, oneof ordinary skill in the art appreciates that various modifications andchanges can be made without departing from the scope of the presentdisclosure as set forth in the claims below. Accordingly, thespecification and figures are to be regarded in an illustrative ratherthan a restrictive sense, and all such modifications are intended to beincluded within the scope of the present disclosure.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims. Moreover, the particular embodimentsdisclosed above are illustrative only, as the disclosed subject mattermay be modified and practiced in different but equivalent mannersapparent to those skilled in the art having the benefit of the teachingsherein. No limitations are intended to the details of construction ordesign herein shown, other than as described in the claims below. It istherefore evident that the particular embodiments disclosed above may bealtered or modified and all such variations are considered within thescope of the disclosed subject matter. Accordingly, the protectionsought herein is as set forth in the claims below.

1. An apparatus comprising: at least one processor; and at least onememory including computer program code; the at least one memory and thecomputer program code configured to, with the at least one processor,cause the apparatus at least to perform: receiving a call request for amission critical, push to talk (MCPTT) call; accessing, in response toreceiving the call request, a mapping of an MCPTT identifier of a userequipment with an interworking identifier that is formed according to anaddress format implemented in Global System for Mobile communications(GSM) for Railways (GSM-R); and forwarding the call request based on themapping.
 2. The apparatus of claim 1, wherein the MCPTT identifier is auniform resource identifier (URI) and the interworking identifier isrepresented in an e164 format.
 3. The apparatus of claim 1, wherein themapping is stored in a user profile that includes a binding between theMCPTT identifier, the interworking identifier, and an identifier of theapparatus.
 4. The apparatus of claim 3, wherein the at least one memoryand computer program code is further configured, with the processor, tocause the apparatus to perform: storing the user profile in a routingtable, and wherein the processor is configured to access the mappingfrom the memory.
 5. The apparatus of claim 3, wherein the at least onememory and the computer program code is further configured to, with theat least one processor, cause the apparatus at least to performaccessing the mapping from a database that is implemented external tothe apparatus.
 6. The apparatus of claim 3, wherein the at least onememory and the computer program code is further configured to, with theat least one processor, cause the apparatus at least to performreceiving the call request including the MCPTT identifier in response tothe user equipment initiating the MCPTT call, and wherein the processoris configured to add the interworking identifier to the call requestprior to forwarding the call request to an interworking functionassociated with a GSM-R system.
 7. The apparatus of claim 6, wherein theinterworking identifier is displayed to a GSM-R client or used toinitiate another call to the user equipment by the GSM-R client.
 8. Theapparatus of claim 3, wherein the at least one memory and the computerprogram code is further configured to, with the at least one processor,cause the apparatus at least to perform receiving the call requestincluding an identifier in the address format implemented in GSM-R inresponse to a GSM-R client initiating a call.
 9. The apparatus of claim8, wherein the at least one memory and the computer program code isfurther configured to, with the at least one processor, cause theapparatus at least to perform resolving the identifier into the MCPTTidentifier of the user equipment, and wherein the transceiver isconfigured to forward the call request to the user equipment based onthe MCPTT identifier.
 10. A method comprising: receiving, at a server, acall request for a mission critical, push to talk (MCPTT) call;accessing, from the server and in response to receiving the callrequest, a mapping of an MCPTT identifier of a user equipment with aninterworking identifier that is formed according to an address formatimplemented in Global System for Mobile communications (GSM) forRailways (GSM-R); and forwarding the call request from the server basedon the mapping.
 11. The method of claim 10, wherein the MCPTT identifieris a uniform resource identifier (URI) and the interworking identifieris represented in an e164 format.
 12. The method of claim 10, furthercomprising: storing the mapping in a user profile that includes abinding between the MCPTT identifier, the interworking identifier, andan identifier of the server.
 13. The method of claim 12, wherein storingthe mapping in the user profile comprises storing the user profile in arouting table implemented in the server, and wherein accessing themapping comprises accessing the mapping from the user profile.
 14. Themethod of claim 12, wherein accessing the mapping comprises accessingthe mapping from a database that is implemented external to the server.15. The method of claim 12, further comprising receiving, at the server,the call request including the MCPTT identifier in response to the userequipment initiating the MCPTT call; adding, at the server, theinterworking identifier to the call request; and forwarding, from theserver, the call request to an interworking function associated with aGSM-R system.
 16. The method of claim 15, further comprising: displayingthe interworking identifier to a GSM-R client.
 17. The method of claim15, further comprising: receiving, at the server, an other call requestfrom a GSM-R client to initiate another call to the user equipment,wherein the other call request includes the interworking identifier. 18.The method of claim 10, further comprising: receiving, at the server,the call request including an identifier in the address formatimplemented in GSM-R in response to a GSM-R client initiating a call.19. The method of claim 18, further comprising: resolving, at theserver, the identifier into the MCPTT identifier of the user equipment;and forwarding, from the server, the call request to the user equipmentbased on the MCPTT identifier.
 20. A non-transitory computer readablestorage medium comprising software with instructions that, when executedby one or more processors, manipulate the one or more processors tocause an apparatus to perform receiving a call request for a missioncritical, push to talk (MCPTT) call; accessing, in response to receivingthe call request, a mapping of an MCPTT identifier of a user equipmentwith an interworking identifier that is formed according to an addressformat implemented in Global System for Mobile communications (GSM) forRailways (GSM-R); and forwarding the call request based on the mapping.